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Wed, 8 Oct 2025 11:57:59 -0700 Date: Wed, 8 Oct 2025 11:57:57 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: , Joerg Roedel , Kevin Tian , Robin Murphy , Will Deacon , Alex Williamson , Joao Martins , , , , Yishai Hadas Subject: Re: [PATCH rc] iommufd: Don't overflow during division for dirty tracking Message-ID: References: <0-v1-663679b57226+172-iommufd_dirty_div0_jgg@nvidia.com> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <0-v1-663679b57226+172-iommufd_dirty_div0_jgg@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS2PEPF0000343C:EE_|CH3PR12MB7594:EE_ X-MS-Office365-Filtering-Correlation-Id: dfde37c2-4704-4574-cbb9-08de069ca336 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|82310400026|36860700013|13003099007; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Oct 2025 18:58:15.4476 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: dfde37c2-4704-4574-cbb9-08de069ca336 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: DS2PEPF0000343C.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB7594 On Wed, Oct 08, 2025 at 03:17:18PM -0300, Jason Gunthorpe wrote: > If pgshift is 63 then BITS_PER_TYPE(*bitmap->bitmap) * pgsize will overflow > to 0 and this triggers divide by 0. > > In this case the index should just be 0, so reorganize things to divide > by shift and avoid hitting any overflows. > > Cc: stable@vger.kernel.org > Fixes: 58ccf0190d19 ("vfio: Add an IOVA bitmap support") > Reported-by: syzbot+093a8a8b859472e6c257@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=093a8a8b859472e6c257 > Signed-off-by: Jason Gunthorpe Reviewed-by: Nicolin Chen